Horrible gas milage...power valve?? - Team Camaro Tech
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post #1 of 27 (permalink) Old Jul 28th, 06, 06:08 AM Thread Starter
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Horrible gas milage...power valve??

Any help appreciated!
small block chev, very mild build with a holley avenger 650 vacume secondary carb. I was getting 15mpg this year since I tuned it with a vacume gauge. I just fixed a bad lifter and that problem is fine now but my milage since putting it back together is less than 10 mpg! I did not touch the carb or even take it off the manifold. My idle is smooth and the car runs well. I spayed carb cleaner all around the minifold looking for a leak but found none. When putting the distributor back in I did get off a tooth or two and I had one hell of a backfire when I hit the key. The Holley avenger has power valve blow out protection but I wonder how fool-proof this is?

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post #2 of 27 (permalink) Old Jul 28th, 06, 06:28 AM
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Re: Horrible gas milage...power valve??

Power valve protection probably does work, checking physically would certainly eliminate this as a problem.

Use a vacuum gauge and adjust carb for best, read hignest, numerical reading. Might recheck initial timing also, maybe add alittle more timing, but not as much as to kick back against the starter when hot.

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post #3 of 27 (permalink) Old Jul 28th, 06, 06:51 AM Thread Starter
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Re: Horrible gas milage...power valve??

How would I check the power valve. This is in the metering block right? Do I take the bowl off? What do I look for if it's blown.

My timing is maxed, any more and the engine chatters at me going up a hill (real low gears!)

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post #4 of 27 (permalink) Old Jul 28th, 06, 08:00 AM
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Re: Horrible gas milage...power valve??

Yes, it is on the metering block and the bowl would have to come off.

Once the plate is off. you will see the power valve. Go to the vacuum side, that part of the plate facing inside and apply suction or blow hard into the valve with your lips & mouth. If valve is good, no air will be sucked or blown through.

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post #5 of 27 (permalink) Old Jul 28th, 06, 12:40 PM Thread Starter
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Re: Horrible gas milage...power valve??

Thanks Everett. I will do that and retune the whole thing this weekend.
Josh

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post #6 of 27 (permalink) Old Jul 28th, 06, 01:09 PM
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Re: Horrible gas milage...power valve??

Just a thought, vacuum advance on distributor is for gas mileage.So maybe if it was old it could of blown out with backfire.
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post #7 of 27 (permalink) Old Jul 28th, 06, 09:52 PM
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Re: Horrible gas milage...power valve??

If you think your PV may be damaged, they cost under $10, so it may be worth to just replace it. It probably has a 65 in it.

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post #8 of 27 (permalink) Old Jul 30th, 06, 05:18 AM
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Re: Horrible gas milage...power valve??

Quote:
Originally Posted by 69-x55
Just a thought, vacuum advance on distributor is for gas mileage.So maybe if it was old it could of blown out with backfire.
Yeah, vacuum advance is crucial for maximum mileage. Just use a timing light and check. I always use a manifold vacuum source, which means there is vacuum at idle. I know there is great debate about this (manifold versus ported), but manifold vacuum is the way to go, IMO.

Set initial timing at around 10 degrees, then when you hook up the vacuum advance, it should jump to about 24 degrees or so.

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post #9 of 27 (permalink) Old Jul 31st, 06, 12:11 PM Thread Starter
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Re: Horrible gas milage...power valve??

I checked the vacume advance before and it was good. I took the carb apart and the PV was good. I cleaned everything including the needle and seat, reassembled and reset float, and mixture, which seemed to be in the right spot anyway. Drove 40 miles yesterday and 15 today and it seems to be much better. Needle just moved off "F" with 55 miles of driving. Something must have been stuck?? Regardless I am happy it's fixed. Thanks guys!

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post #10 of 27 (permalink) Old Jul 31st, 06, 07:27 PM
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Re: Horrible gas milage...power valve??

55 miles and just off of FULL. I get 55 ft and I can see my gauge go down. LOL.

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post #11 of 27 (permalink) Old Aug 1st, 06, 03:33 AM
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Re: Horrible gas milage...power valve??

It wanted you to feel it. Don't you hate that? Tear it all apart and find nothing wrong, but assemble it and it works fine?

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post #12 of 27 (permalink) Old Aug 1st, 06, 06:16 AM Thread Starter
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Re: Horrible gas milage...power valve??

Yea, it wants me to know who is boss!

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post #13 of 27 (permalink) Old Aug 1st, 06, 09:10 AM
 
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Re: Horrible gas milage...power valve??

this might not be your problem but if it is your in luck super easy fix, my camaro (86 2.8L V6 MPI) started getting horrible gas milage, seemed like i would drive around the block and use an eigth of a tank, i replaced my O2 sensor, and it gets better gas milage than it did when i bought it, may not be your problem, but hope it helps
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post #14 of 27 (permalink) Old Aug 11th, 06, 08:13 AM
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Re: Horrible gas milage...power valve??

throw the holley in the craper
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post #15 of 27 (permalink) Old Aug 11th, 06, 09:02 AM
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Re: Horrible gas milage...power valve??

Vacuum advance on the distributor has little to do with gas milage. What it does do is provide for easier starting and give the engine a bit more oomph upon take off. At cruising speeds, vacuum advance should be barely functional anyway. I wouldn't spend too much time worrying about vacuum advance. The power valve on the other hand is a possibility.

To check the power valves and vacuum advance, I use a hand vacuum pump (about $15 at any auto supply place). I have a rubber suction cup from one of my kids toys that I place on the back of the power valve to see if I can pull and hold a vacuum on it. Also make sure the gasket around the power valve hasn't fallen out of place. You do have to remove the bowl / metering block to access the power valves.

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